1. Field of the Invention
The present invention relates to a vehicle brake device.
2. Discussion of the Related Art
Heretofore, brake devices for vehicles of this kind, there has been known one which is provided with a master cylinder for generating a fluid pressure depending on the stepping state of a brake pedal and a pressurized fluid supply source which is provided separately from the master cylinder for supplying pressurized fluid to brake cylinders of wheels. In the brake device, the pressurized fluid supply source supplies the brake cylinders with pressurized fluid depending on the stepping state of the brake pedal in the normal state thereof, while the master cylinder which is operatively connected to the brake pedal supplies pressurized fluid required for the brake cylinders in the abnormal state of the pressurized fluid supply source. The vehicle brake device is provided with a stroke simulator for enabling the brake pedal to move through a stroke corresponding to the stepping state of the brake pedal in the normal state of the pressurized fluid supply source.
As the stroke simulator, as described in Japanese unexamined, published patent application No. 2002-293229 (patent document 1), there have been known one which is composed of mechanical components such as a piston 14, a retainer member 17, multiple springs 19, 20, a rubber cushion 21 and the like and which is capable of setting a reaction force property of the pedal in dependence on stroke amounts of the piston 14 and the retainer member 17 which work as movable parts and also in dependence on the resilient forces of the multiple springs 19, 20 and the rubber cushion 21. In this case, there can be attained different pedal feelings required for various vehicle models. However, the mechanical components constituting the stroke simulator have to be changed for alteration of the reaction force property, so that once set, the reaction force property cannot be altered easily. Further, since the stroke simulator is of the type which is composed of mechanical components, the non-uniformity in the reaction force property may be given among stroke simulators by the causes of the errors in assembling the components and other errors. This gives rise to another problem that the reaction force property cannot be adjusted easily.
As described in Japanese unexamined, published patent application No. 11-341604 (patent document 2), there has been proposed another brake device which is provided with an solenoid open/close valve (changeover valve) between a master cylinder and a stroke simulator and which is capable of adjusting the reaction force property of a brake pedal by controlling the open/close operation of the solenoid open/close valve. In addition, as described in Japanese translation 2000-507188 of PCT international application (patent document 3), there has been proposed still another brake device which is provided with a proportionally controlled solenoid valve and a low-pressure fluid accumulator in substitution for a stroke simulator not provided therein and which is capable of adjusting the reaction force property of a brake pedal by controlling the open/close operation of the proportionally controlled solenoid valve.
In the invention described in the patent document 2, the solenoid open/close valve (changeover valve) 14 of the normally closed type is provided between the master cylinder 1 and the stroke simulator 15, and the duty control of the solenoid open/close valve 14 is performed in dependence on the stepping amount of the brake pedal 2. More specifically, the duty control is performed in such a way that when the stepping amount of the brake pedal 2 is less than a predetermined value, the solenoid open/close valve 14 is kept around in a full-open state to make the variation amount in the brake pedal stroke larger relative to an increase in the brake pedal stepping force and that when the stepping amount of the brake pedal 2 increases to the predetermined value or larger, the solenoid open/close valve 14 is kept around in the closed state to make the variation amount in the brake pedal stroke smaller relative to an increase in the brake pedal stepping force. In this way, the flow volume flowing toward and away from the stroke simulator 15 is suppressed to change the reaction force of the brake pedal 2 dynamically.
Further, in the invention described in the patent document 3, two pedal path valves 32, 34 (constituted by proportional direction control valves or proportional pressured regulating valves) are provided together with low-pressure and high-pressure accumulators 20, 24 and a fluid pump 18 to constitute an active pedal-path simulator for power braking. During the power braking, a shut-off valve 14 is closed, whereby the brake fluid cannot be exhausted from a master brake cylinder 10 toward wheel brake cylinders 16. To obtain the pedal path nevertheless, the pedal path valve 34 arranged on a suction side of the fluid pump 18 is opened until a desired pedal path is attained. To return the brake pedal 46, the pedal path valve 32 arranged on an ejection side of the fluid pump 18 is opened, whereby the brake fluid is flown from the high-pressure accumulator 24 into the master brake cylinder 10 to return the same together with the brake pedal 46 to their home positions.
The pedal path measured by a pedal path sensor 44 is adjusted in dependence on the pressure which is generated in the master brake cylinder 10 in dependence on the stepping force of the brake pedal 46 and which is measured by a stepping force sensor 42. A desired stepping force to path property curve can be adjusted in this manner. Further, the stepping force to path property curve can be easily varied by changing an adjusting algorithm which enables an electronic control device 54 to control the pedal path valves 32, 34. In this case, any change is not required regarding the mechanical components for fluid control in the vehicle brake device. Therefore, it becomes possible easily to adapt the vehicle brake device to various vehicle models.
In the aforementioned vehicle brake device described in the patent document 2, by performing the duty control of the solenoid 14 in dependence on the pedal stepping amount, the flow volume which is flown toward and away from the stroke simulator 15 is suppressed, so that the reaction force given to the brake pedal 2 is changed dynamically. However, when the solenoid open/close valve 14 is switched from a holding state (closed state) that is the state of the duty ratio being 0 (zero) percent, again to an open state, the delay in operation of the solenoid open/close valve 14 occurs by the cause of the duty control. This may result in bringing about an inoperative braking state in which the brake pedal 2 is tried to be stepped on, but does not move at that moment.
Also, in the aforementioned vehicle brake device described in the patent document 3, it can be realized to remove any mechanical type simulator as described in the patent document 1. However, instead, it is required to provide the two pedal path valves 32, 34 and the low-pressure accumulator 20. This causes the brake device to be increased in the number of the components and therefore, makes the brake device raised in cost and enlarged in dimensions.